FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically ceramic beams shaped in the form of a U that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi, αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape bearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. The wrap angles αi, αo and tape bearing surface 112 are often adjusted to deal with various operational aspects of heads such as that of FIG. 1.
FIG. 2A is an enlarged view of the area encircled in FIG. 1. During use of the head of FIG. 1, various effects traditionally occur. With reference to FIG. 2A, a first known effect associated with the use of the head 100 is that when the tape 108 moves across the head as shown, air is skived from below the tape 108 by a skiving edge 204 of the substrate 104A. Instead of the tape 108 lifting from the tape bearing surface 109 of the module (as intuitively it should), the reduced air pressure in the area between the tape 108 and the tape bearing surface 109 allows atmospheric pressure to urge the tape towards the tape bearing surface 109.
To obtain this desirable effect, the wrap angle αo is carefully selected. An illustrative wrap angle is about 0.9°±0.2. Note, however, that any wrap angle greater than 0° results in tents 202 being formed in the tape 108 on opposite edges of the tape bearing surface 109. This effect is a function of tape stiffness and tension. For given geometrical wrap angles for example, stiffer tapes will have larger tents 202.
If the wrap angle αi, αo is too high, the tape 108 will tend to lift from the tape bearing surface 109 in spite of the vacuum. The larger the wrap angle, the larger the tent 202, and consequently the more air is allowed to enter between the tape bearing surface 109 and tape 108. Ultimately, the forces (atmospheric pressure) urging the tape 108 towards the tape bearing surface 109 are overcome and the tape 108 becomes detached from the tape bearing surface 109.
As shown in FIG. 2B, if the wrap angle αi, αo is too small, the tape tends to exhibit tape lifting 205, or curling, along the side edge of the tape bearing surface 109. This is a result of air leaking in at the edges and tape mechanical effects. Particularly, the edges of the tape tend to curl away from the tape bearing surface 109, resulting in edge loss or increased spacing between the edges of the tape and the tape bearing surface 109. This is undesirable, as data cannot reliably be written to the edges of a tape in a system subject to edge loss.
Additionally, the tape lifting 205 results in additional stress at points 206 which, in turn, may cause additional wear of the head. Further augmenting such tape lifting 205 is the fact that the tape 108 naturally has upturned edges due to widespread use of technology applied in the video tape arts.
The external wrap angles αo are typically set in the drive, such as by rollers. The offset axis creates an orbital arc of rotation, allowing precise alignment of the wrap angle αo. However, situations arise where rollers may not be the most desirable choice to set the external wrap angles αo. For example, rollers require extra headroom in a drive, particularly where they are adjustable. Additionally, rollers, and particularly adjustable roller systems, may be more expensive to install in the drive. A further drawback of this approach is mechanical alignment cannot be completed independent of signal read readiness.
FIG. 3 illustrates one proposed solution to set the desired external wrap angles αo, and which may be less expensive than implementing adjustable rollers. The proposed solution comprises forming outriggers 150 on the module 104, as shown in FIG. 3. The outriggers 150 set the external wrap angles αo. However, as the fabrication of tape head components moves towards use of thinner wafers, the distance between the front and back faces of the module 104 is reduced. When outriggers 150 are used, a minimum free space span between the outrigger inner edge 152 and the outer edge 154 of the primary tape bearing surface 109 is required to compensate for the aforementioned tape effect, namely tenting. Particularly, in a flat-profile tape head (as shown), the elements 106 are positioned between the substrate 104A and a closure 104B. The primary tape bearing surface 109 needs to be long enough in the direction of tape travel so that tenting does not occur over the elements 106, because reliability of the read/write functions depends in part on the tape-head spacing.
Because of the requisite length of the primary tape bearing surface 109, in combination with the fact that the bending moment of the tape propagates out from the outrigger, the distance between the outer edge 154 of the primary tape bearing surface and the back end 158 of the substrate 104A becomes too small to accommodate an outrigger. Accordingly, it will not be possible to create and outrigger on the same substrate on which the transducers are formed in the next generation of heads.
Another difficulty created by the reduced span is that the height of the outrigger must be kept to a very tight tolerance to maintain the proper wrap angle, as the shorter distance between outrigger and primary tape bearing surface means there is less room for deviation.
There is accordingly a clearly-felt need in the art for a tape head assembly in which the critical wrap angles are fixed on the head assembly itself. There is also a clearly-felt need for a way to provide an outrigger on a tape head assembly of small proportions.